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Zusammenfassung:
The static and dynamic magnetic properties of tetragonally distorted
Mn-Ga based alloys were investigated. Static properties are determined
in magnetic fields up to 6.5 T using SQUID magnetometry. For the pure
Mn1.6Ga film, the saturation magnetisation is 0.36 MA m(-1) and the
coercivity is 0.29 T. Partial substitution of Mn by Co results in
Mn2.6Co0.3Ga1.1. The saturation magnetisation of those films drops to
0.2 MA m(-1) and the coercivity is increased to 1 T.
The time-resolved magneto-optical Kerr effect (TR-MOKE) is used to probe
the high-frequency dynamics of Mn-Ga. The ferromagnetic resonance
frequency extrapolated to zero-field is found to be 125 GHz with a
Gilbert damping, alpha, of 0.019. The anisotropy field is determined
from both SQUID and TR-MOKE to be 4.5 T, corresponding to an effective
anisotropy density of 0.81 MJ m(-3).
Given the large anisotropy field of the Mn2.6Co0.3Ga1.1 film, pulsed
magnetic fields up to 60 T are used to determine the field strength
required to saturate the film in the plane. For this, the extraordinary
Hall effect was employed as a probe of the local magnetisation. By
integrating the reconstructed in-plane magnetisation curve, the
effective anisotropy energy density for Mn2.6Co0.3Ga1.1 is determined to
be 1.23 MJ m(-3).
